The present invention relates to a method and a device for power management in a display unit such as a PC monitor which uses a CRT for information display.
The electrical energy consumed by a video display is mostly, if not completely, converted into heat energy that warms up the room in which the display device is placed. The conversion of electrical energy into heat energy in this way is indeed wasteful, especially when the video display is not being used to provide any visual information.
It is well-known that PC monitors are generally provided with a power saving scheme such that when the PC is not in use after a certain period of time, the power supply in the monitor will be switched from a regular xe2x80x9cONxe2x80x9d mode to a suspend mode or a stand-by mode to save energy. One of the known standards for power saving is the VESA Display Power Management Signaling (DPMS) Standard. With the VESA standard, the video display is put into different energy-saving states by means of a coded message, based on the present status such as the presence or absence of the vertical sync and horizontal sync signals, as shown in Table 1. With the presence or absence of the video sync signals in different combinations, there are four possible power level states to be set. The ON state is referred to when the display is in full operation, being used to show an image. In the Stand-by state, no image is shown and the power consumption is somewhat reduced while allowing the CRT to return to normal quickly once the PC is again active. In the Suspend state, no image is shown and the power consumption is further reduced but the recovery time for the CRT is longer. In the OFF state, the display is non-operational but a very low level of power is maintained to keep certain electronic components active. These power saving states are further summarized in Table 2, according to the Advance Power Management (APM) specification. The APM specification is set forth by the computer industries for the power management of personal computers, and the specification is provided in the system BIOS, operating system or application software.
In an integrated display unit, in addition to the video display, some audio-visual components such as audio amplifier, speakers, microphone, camera and telephone handset may also be included. Integrated display units are also referred to as xe2x80x9cmultimedia terminalsxe2x80x9d. Like the CRT, the added-on components require adequate electrical power to function properly. Currently, audio components and the camera in an integrated display unit draw power from separate power supplies. These extra power supplies not only increase the cost of an integrated display unit, but also require more space and more power outlets. Therefore, it is desirable to allow these added-on peripheral devices to share a power supply with the CRT. With these added-on components, however, it may not be appropriate to switch the power supply to different power saving states based solely on the present status, e.g., the presence or absence of the video sync signals. Even when the PC is not in an active mode, e.g. the keyboard or the mouse has not been used for a prolonged period, it should not be assumed that all the peripheral devices are also inactive. For example, in a teleconferencing environment, the PC may be completely inactive for a long period of time while the camera is still taking pictures of the conference participants and the audio components are still processing the conversation of the participants. In that case, the power supply in the integrated display unit should not be caused to enter a low power output state that may render the camera and the audio components non-operational. Also, when an integrated display unit is connected to a Universal Serial Bus (USB) hub, or when the integrated display unit is used as a USB hub, the power supply in the integrated display unit should be controlled differently. Furthermore, if the video display in an integrated display unit is also used to display the images acquired by an added-on camera, the image signals from the camera should also be considered as part of the video sync signals.
It is advantageous to provide a method and a device to control the power consumption in an integrated display unit that includes one or more peripheral devices, wherein the peripheral devices may be kept active even when one or more of the video synchronization signals are not present for a certain period of time.
It is an objective of the present invention to provide a method and a device to reduce the consumption of electrical power by an integrated display unit and to make power management more practical.
This objective can be achieved by reducing the number of power supplies in an integrated display unit, preferably to one, and by providing a power management strategy based on the signals associated with the peripheral devices as well as the video sync signals. Preferably, the power management strategy, according to the present invention, is in compliance with the VESA DPMS Standard, as summarized in Table 3.
In accordance with the Power Management Summary as shown in Table 3, there are five power consumption states, POWER ON, STANDBY, SUSPEND, PD (Peripheral Device) and PWR OFF, with each state having a different level of power consumption. It is understood that these power consumption states exist only after the power switch of the integrated display unit has been turned on. If the power switch is not turned on, the external electrical power source to the power supply is completely cut off, as denoted by the xe2x80x9cKEY OFFxe2x80x9d state.
The implementation of different power consumption states is determined by the status, e.g., the presence or absence of the various signals sensed by a plurality of signal detectors in the integrated display unit as described below:
The POWER ON state is implemented when both the horizontal sync signal and the vertical sync signal are present. In this state, video images are shown on the display and the power consumption for example which follows is about 130 W.
The STANDBY state is implemented when the vertical sync signal is present but the horizontal sync signal is not present. Even though no video image is shown, the CRT remains heated for quick recovery. The power consumption is reduced to about 90 W by switching video power amplifier off thereby blanking video output.
The SUSPEND state is implemented when the horizontal sync signal is present but the vertical sync signal is not present. No video image is shown. The CRT filament is heated at a much lower voltage level to save energy and deflection is turned off. The total power consumption is thereby further reduced to about 10 W.
The PD state is implemented when signals associated with one or more peripheral devices, including a USB signal, are present but both the horizontal sync signal and the vertical sync signal are absent. The CRT filament is not heated. Power consumption is typically 8 W, but it can be more or less depending on the peripherals in the integrated display unit.
The PWR OFF state is implemented when no incoming signals are present. The power consumption of about 5 W is mainly for keeping signal detectors active. If there is an audio preamplifier in the integrated display unit, it is preferable to keep the preamplifier operational. However, generally this is not required.
In order to effect the power reduction in different power consumption states, the power supply is caused to enter different output modes. According to the present invention, the output modes include at least a high-output mode and a suspend output mode. The power supply is in the high-output mode when the power consumption level is either at the POWER ON or the STANDBY state. The power supply is in the suspend output mode when the power consumption level is either at the SUSPEND or the PD state. The power supply is caused to enter different output modes based on the status, e.g., the presence or absence of various signals as described in the following:
The power supply is caused to enter the high output mode whenever the vertical sync signal is present;
the power supply is caused to enter the suspend output mode when the vertical sync signal is not present but one or more of the other signals are present;
the power supply is electronically turned off when no incoming signals are present.
As can be seen from Table 3, the implementation of the power consumption states and the output modes of the power supply are effected by three control signals: Pwr_{overscore (u)}, Pwr_o, and Pwr_{overscore (s)}. These control signals are produced by a variety of signal detectors which sense the presence of the video sync signals and the peripheral signals.
The Pwr_{overscore (u)} signal is set at a xe2x80x9c0xe2x80x9d or LOW state when any peripheral signal is present, and at a xe2x80x9c1xe2x80x9d or HIGH state when no peripheral signals are present.
The Pwr_o signal is set at a xe2x80x9c1xe2x80x9d or HIGH state when any of the horizontal sync signal, the vertical sync signal and the peripheral signal is present, and at a xe2x80x9c0xe2x80x9d or LOW state when none of these signals are present.
The Pwr_{overscore (s)} signal is set at a xe2x80x9c1xe2x80x9d or HIGH state only when the vertical sync signal is present.
The method and device for effecting the reduction of power consumption in an integrated display unit will become apparent upon reading the drawings and the accompanying descriptions.